Nano- and micro-motors used in biomedical applications and many low-cost nanofabrication processes typically comprise a variety of micro and/or nanoparticle composites capable of propelling towards or away from a source field. Inorganic nanomotors based on different propelling mechanisms including, for example, self-electrophoresis, self-diffusiophoresis, bubble propelling, and self-acoustophoresis, have been demonstrated in the past.
To remotely control nano- and micro-motors, the use of ferromagnetic materials has been commonly incorporated in the motors and can be steered and/or directed in response to an external magnetic field. On the other hand, optical manipulation such as optical tweezers has also been found useful in controlling nanoscale machines since optical field can be designed and manipulated with better precision and accuracy. Collective phototactic behavior has been observed in synthetic inorganic Janus nanoparticles, which suggested the potential of designing optically controlled nanorobots. However, in order to design fully functional nanorobots based on phototaxis phenomenon, it is critical to design individual nanomotors whose motion can be tuned and programmed.